Secondary batteries (e.g., rechargeable batteries) are actively researched due to development of portable electronic devices such as, for example, E-bikes, E-scooters, and power and gardening tools. FIG. 1 schematically shows a traditional battery pack 100. As shown in FIG. 1, the battery pack 100 comprises a battery 10, a charge and discharge circuit 20, a battery management system (BMS) 30, an external pre-bias circuit 40 and pack terminals 50.
The battery 10 may include one or more battery cells 11, which may be a rechargeable secondary battery. The charge and discharge circuit 20 including a charging switch 101 and a discharging switch 102 is arranged between the battery 10 and the pack terminals 50. The BMS 30 is coupled to the battery 10 and is configured to generate a charging control signal CHG and a discharging control signal DSG to control the charging switch 101 and the discharging switch 102, respectively. The battery pack 100 may be coupled with a load or an external power source via the pack terminals 50. When the external power source is connected to the battery pack 100 via the pack terminals 50, the battery 10 is charged through the charging switch 101 and the charging switch 102 or its parasitic diode D2. When the load is connected to the battery pack 100 via the pack terminals 50, the discharge to the load is performed through the charging switch 101 or its parasitic diode D1 and the discharging switch 102. The load may be a motor driven device such as an E-bike including a capacitor 60 charged by the battery pack 100 and a motor driven by the electrical charge stored in the capacitor 60. As shown in FIG. 1, the capacitor 60 is connected between a positive pack terminal P+ and a negative pack terminal P− in parallel to the battery pack 100.
When the motor driven device, such as an E-bike, is turned OFF for quite some time, the capacitor 60 is fully discharged and there is no electrical charge in the capacitor 60, as a result, the voltage across the capacitor 60 is 0V. Then when the discharging switch 102 is turned ON by the BMS 30, typically after turning ON of the charging switch 101, the capacitor 60 coupled between the pack terminals 50 tends to receive an excessive current that can cause damage or trip over current protection. To mitigate these issues, the external pre-bias circuit 40 is typically present so that the excessive current flowing into the capacitor 60 is prevented when the capacitor 60 is fully discharged, that is when there is no accumulated electrical charge in the capacitor 60. As shown in FIG. 1, the external pre-bias circuit 40 typically includes a current limiting switch 103 and a current limiting resistor 104 to avoid the excessive current flowing into the capacitor 60. The external pre-bias circuit 40 is typically located on the printed circuit board of the BMS 30 and then is combined with the battery pack 100.
However, there are undesired drawbacks such as two additional off-chip components resulting in additional cost and PCB area, and longer than the desired battery pack turn-on time, since the battery pack turn-ON time is limited by an RC profile dictated by the capacitor 60 and the current limiting resistor 104.